Device for lighting filament lamp

ABSTRACT

To eliminate the effect of high-frequency distortion on the power supply side in filament lamp lighting devices that perform light adjustment of multiple filament lamps. In a filament lamp lighting device that has an alternating current power supply connected to the input side and lights multiple filament lamps by controlling its output power, in 
     Lamp lighting control circuits 2-1 through 2-n are established to respond to multiple filament lamps 4-1 through 4-n. When their switching elements are ON, these lighting control circuits 2-1 through 2-n supply input current to the filament lamps 4-1 through 4n; when the switching element is OFF, current continuous to flow to the filament lamp by means of energy stored in an inductance L. Subsequent alternation of the ON and OFF states supplies the filament lamp with output current with roughly the same shape as the input current waveform. 
     Moreover the controller 3, by varying the duty cycle of the ON/OFF signals of the switching elements, varies the peak values of the output current and also provides the lighting control circuits 2-1 through 2-n with ON/OFF signals having staggered timing.

FIELD OF TECHNOLOGY

This invention concerns a filament lamp lighting device for such uses asgeneral lighting or heat: treatment equipment. In more detail, itconcerns a filament lamp lighting device that connects to the filamentlamp on the output side and controls the output power.

BACKGROUND OF TECHNOLOGY

Filament lamp lighting devices are widely used for heat treatment andgeneral lighting. Light irradiation heat treatment equipment forsemiconductor wafers (hereafter wafers) can be cited as one applicationof filament lamp lighting devices to heat treatment.

Heat treatment is used in the process of semiconductor manufacturing forrapidly heating wafers, maintaining them at a high temperature, andrapid cooling. It is carried out in a broad range of processes such asfilm formation, diffusion and annealing.

In all the above processes, the wafer is treated at a high temperature,and when this heat treatment is done using light irradiation heattreatment equipment, the wafer can be heated rapidly, exceeding 1000° C.in 10 to 30 seconds. And when the light irradiation is stopped, rapidcooling is possible.

However, if the temperature distribution of the wafer is uneven when thewafer is heated, the phenomenon known as slip occurs in the wafer. Inother words, defects occur in the crystal dislocation, and poor qualityproducts are liable to result.

Therefore, when using light irradiation heat treatment equipment forheat treatment of wafers, it is necessary that the heating, temperaturemaintenance and cooling of the wafer be done with uniform temperaturedistribution.

Light irradiation heat treatment equipment intended to irradiate so thatthe temperature distribution of the wafer will be uniform includes, forexample, that presented in JPO kokai patent report H8-45863. The lightsource of the light irradiation heat treatment equipment described inthat report had a number of ring-shaped infrared lamps of differentdiameters arranged in concentric circles. By arranging the lights inthat way, the wafer could be divided into concentric zones, andtemperature control was simplified.

To make the temperature of the wafer uniform, the temperature of eachzone of the wafer was measured and the heat generated by the infraredlamp corresponding to each zone was controlled accordingly. That is, ifthe temperature were lower at the periphery of the wafer, the inputpower to the lamp covering the center of the wafer would be increased,and the amount of heat generated by the lamp would go up and apply moreheat to the wafer. The variation of the heat generated by the lamp isreferred to below as “light adjustment.”

Halogen lamps with filaments that radiate infrared light efficiently aregenerally used as the infrared lamps in light irradiation heat treatmentequipment. Moreover, an alternating current power supply is generallyused as the lighting power supply.

Light adjustment of filament lamps is done in the following way.

(1) For light adjustment of a filament lamp in a general lightingfixture, a circuit with a triac is normally used, and adjustment is doneby controlling the continuity angle of the triac.

(2) Light adjustment of light irradiation heat treatment equipmentbasically applies the same circuit, and so a thyristor is used. Thebasic structure of lamp lighting device using thyristors is shown inFIG. 9. Now, one lamp lighting device is used for a single lamp.Consequently, in equipment to control the lighting of multiple lamps,the number of lamp lighting devices depends on the number of lamps. Thedevices are housed on the equipment power supply box.

In the lighting device shown in FIG. 9, control of the power input tothe lamp, or light adjustment, is done by varying the timing of the gatecurrent of thyristors SCR1 and SCR2.

Power control by thyristor is done by two methods, continuity anglecontrol and zero cross control. Now, terminology is defined below. Inputpower from a commercial alternating current power supply to the lamplighting device is called “input.” The power output from the lamplighting device to the lamp is called “output.” Accordingly, “outputpower” is “lamp input power.”

(a) Continuity Angle Control

In FIG. 9, alternating current from a commercial alternating currentpower supply 21 is input to the lamp lighting device 100. Within thelamp lighting device 100 is a lamp lighting control circuit 200 thatcomprises the first thyristor SCR1 and the second thyristor SCR2. Whenthe gate signal generated by the gate signal generation circuit of thecontroller 300 lets the gate current flow to the gates G1, G2 of thethyristors SCR1, SCR2 of the lamp lighting control circuit 200, thencurrent is output from the lamp lighting device 100 to the lamp 23 untilthe current supplied to the thyristors SCR1, SCR2 of the lamp lightingcontrol circuit 200 becomes zero.

FIG. 10 is a diagram showing the various waveforms in the event ofcontinuity angle control of the thyristors in FIG. 9. FIG. 10(a) showsthe input voltage waveform to the lamp lighting device 100. FIG. 10(b)is a diagram showing an example of the timing of the gate current flowto the gates G1, G2 of the thyristors SCR1, SCR2, in which (1) is thegate current for the first thyristor SCR1 and (2) is the gate currentfor the second thyristor SCR2. FIG. 10(c) shows the waveform of theoutput current when the gate current flows with the timing from FIG.10(b). Now, in the case of filament lamp lighting devices, the outputvoltage has the same waveform as the output current.

Consequently, the output power from the lamp lighting device 100 is theproduct of the out current waveform and the output voltage waveformshown by the shaded area of FIG. 10(c). By varying the timing of thegate current supplied to the thyristors SCR1, SCR2, it is possible tovary the output voltage waveform an output current waveform shown inFIG. 10(c), and so light adjustment that varies the output power, whichis the lamp input power, is possible.

(b) Zero Cross Control

FIG. 11 is a diagram showing the various waveforms in the event of zerocross control of the thyristors in FIG. 9. The structure of the controlcircuit is the same as FIG. 9, and the timing of the gate current to thethyristors SCR1, SCR2 is as shown in FIG. 11(b). In the figure, (1) isthe gate current for the first thyristor SCR1 and (2) is the gatecurrent for the second thyristor SCR2.

FIG. 11(c) shows the output current and output voltage when the gatecurrent has the timing shown in FIG. 11(b). As shown in FIG. 11(c), thelamp input voltage is varied and light adjustment is carried out bymeans of intermittence of output current and output voltage waveforms.

However, the two control methods described above have the followingproblems.

(1) Occurrence of Transient Noise (Continuity Angle Control)

In the continuity angle control method illustrated in FIG. 10, a highvoltage is suddenly impressed on the lamp as shown in FIG. 10(c).Because of that, noise known as transient noise occurs within the lamplighting device, and that sometimes causes the device control system tomalfunction. And because of a rush current flow in the lamp filament,the filament is in a state of overload, which is liable to causefilament breakage.

(2) Drop in Response Speed; Lack of Constant Control (Zero CrossControl)

In the case of zero cross control, the voltage of the power source issent through the thyristor at the time of the zero cross, so a highvoltage is not impressed suddenly on the lamp. Nevertheless, the cyclesof the commercial input frequency are thinned out as shown in FIG. 11(b)so the response time of the light adjustment cannot be faster than thefrequency of the commercial power supply, and rapid light adjustment isnot possible. Moreover, the output power cannot be varied continually,and so minute light adjustment is not possible.

(3) Occurrence of High-frequency Distortion

Taking the example of continuity angle control shown in FIG. 10, whenthe power control is done on the output side, as described above, theoutput voltage and output current are as shown in FIG. 12(a) and (b)respectively.

On the other hand, the waveform of the input voltage to the lamplighting device 100 is the voltage waveform of the commercialalternating current power supply shown in FIG. 12(c). The waveform ofthe input current, moreover, is the same as the waveform of the outputcurrent, as shown in FIG. 12(d).

The following problem occurs when the input current has this kind ofwaveform. The parts of the waveform indicated by the circles in FIG.12(d) are nonlinear, and that causes high-frequency distortion of theinput current. This sort of high-frequency distortion is becoming theobject of regulation.

A similar problem occurs in the zero cross control illustrated in FIG.11. The parts of the waveform indicated by the circles in FIG. 12(e) arenonlinear, and high-frequency distortion occurs.

(4) Occurrence of Reactive Power

In FIG. 12, input voltage is V and input current is I. When W iseffective power and V×I is apparent power, the input voltage waveformand the input current waveform are both sine waves, and are in thefollowing relationship unless there is a phase shift.

V×I=W

W can be thought of as the output power (lamp input power).

However, in the case of a distorted waveform, as in FIG. 12(d), there isalways reactive power (=V×I−W). Consequently, in the distorted waveformshown in FIG. 12(d), in order to output effective power W, it isnecessary to supply an apparent power V×I that is greater than the sinewave.

Similarly in the case of zero cross control, reactive power occursbecause the period shown by the arrows in FIG. 12(e) is considered onecycle.

This reactive power occurs as soon as the output power is controlled.This fact is a big problem when practical equipment is manufactured.

That is, for the reasons given below, the output power of the lamplighting device 100 is always controlled, so there is necessarilyreactive power in the lamp lighting device 100, which harms theefficiency of the lamp lighting device.

1) In practical terms, in equipment such as light irradiation heattreatment equipment, when there is, for example, a commercial 200 Vinput to the lamp lighting device, then considering a 10% voltagefluctuation it is common sense to use a lamp with a rated input voltagethat is 10% lower, 180 V for example, to leave an adequate margin.Consequently, the power of the lamp lighting device is controlled evenwhen lighting the lamp at the rated value.

2) In light irradiation heat treatment equipment, moreover, the lightingand light adjustment of multiple lamps may, depending on the lamps used,involve different ratings (different filament lengths). In this case aswell, the output power is always controlled.

However, an alternating current chopper control method has been proposedas a method to resolve this problem of reactive power. The alternatingcurrent chopper control method is one which controls the output voltage(current) by chopping the input voltage (current) with a switchingcircuit. By controlling the ON period in the switching operation, it ispossible to control the output voltage (output current).

Parts of the waveform when the alternating current chopper controlmethod is in use is shown in FIG. 13.

That is, the input voltage (current) shown in FIG. 13(a) is turnedON/OFF by the switching signal shown in FIG. 13(b), yielding the outputcurrent shown in FIG. 13(c). Now, the figure shows a duty cycle of about50%. In the constitution used here, the switching circuit used forcommutation is in parallel with the load, and the inductance is inseries with the filament lamp, so when the switching circuit connectedin series with the input side is off, the switching circuit forcommutation is on, and the output current flows continuously through thecommutation circuit.

With the waveform shown in FIG. 13(c), if the frequency of the switchingsignals is increased, the waveform becomes closer to a sine wave, and byapplying further filtering to the output current shown in FIG. 13(c), itis possible to obtain the sinusoidal output shown in FIG. 13(d). Theinput current can also be made sinusoidal by passing it through alow-pass filter.

Using the alternating current chopper control method described above, itis possible to have sinusoidal input and output waveforms and, since thephase of the voltage and current is the same, there is no problem ofreactive power.

Moreover, since there is no sudden rise of output current, the problemof rise noise does not occur, and by controlling the duty cycle of theswitching signals, rapid and minute light adjustment is possible.

As stated above, in a lamp lighting device that controls the heatgenerated by a filament lamp by varying the power input to the lamp, itis necessary to vary the output power so as to not impress voltage onthe lamp suddenly (to avoid producing noise and to avoid a large rushcurrent to the lamp), and so as to enable continuous light adjustmentwith a rapid response time. It is also necessary to vary the outputcurrent such that there is no high-frequency distortion of the inputcurrent and no reactive power.

When the alternating current chopper control method described above isused, it is possible to make the output current, output voltage andinput current waveforms sinusoidal, and so continuous light adjustmentwith a rapid response time is possible with no occurrence of reactivepower and without large rush currents being passed suddenly to the lamp.

Nevertheless, the alternating current chopper control method does causehigh-frequency distortion of the input current unless there is a filtercircuit on the input side since, as shown in FIG. 13, the switchingsignals shown in FIG. 13(b) turn the input voltage (current) ON and OFF.

In light irradiation heat treatment equipment, in particular, lightadjustment of multiple filament lamps is necessary and the input currentto be switched is large, so high-frequency distortion has a great effecton the power supply side.

This invention was made in consideration of the situation describedabove. It provides a filament lamp lighting device that has analternating current power supply connected to the input side and lightsmultiple filament lamps by controlling its output power, in which eitherthere is no need for a filter circuit to eliminate high-frequencydistortion on the input side, or it can be miniaturized so that thepower supply side is unaffected by high-frequency distortion.

SUMMARY OF THE INVENTION

In this invention, the problems described above are resolved in thefollowing way.

In a filament lamp lighting device that has an alternating current powersupply connected to the input side and lights multiple filament lamps bycontrolling its output power, in which there is a lighting controlcircuit to respond to each of multiple filament lamps, as well as acontroller to control those lighting control circuits.

These lighting control circuits contain switching elements that switcheither the sinusoidal current provided by the alternating current powersupply or a fully rectified current. When this switching element is ON,input current is supplied to the filament lamp; when the switchingelement is OFF, current continues to flow to the filament lamp by meansof energy stored in an inductance element connected in series with thefilament lamp. Subsequent alternation of the ON and OFF states suppliesthe filament lamp with output current with roughly the same shape as theinput current waveform.

Moreover the controller, by varying the duty cycle of the ON/OFF signalsof the switching elements, varies the peak values of the output currentand also provides the lighting control circuits with ON/OFF signalshaving staggered timing.

In this invention, the ON/OFF signals provided to the individuallighting control circuits have staggered timing, as mentioned above, andso either there is no need for filter circuits or they can beminiaturized, the waveform of the input current within the filament lamplighting device as a whole can be made sinusoidal, and there is noeffect of high-frequency distortion on the power supply side. For thisreason it is possible to simplify the constitution of the equipment andto reduce costs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing the constitution of the filament lamplighting device of the first implementation of this invention.

FIG. 2 is a diagram showing the constitution of the lamp lightingcontrol circuit of the first implementation of this invention.

FIG. 3 is a diagram to explain the gate signals that drive the switchingelements of the lighting control circuits.

FIG. 4 is a diagram showing an example of the timing of gate signalsprovided to lighting control circuits 2-1 through 2-n.

FIG. 5 is a diagram showing the input current waveform when multiplelighting control circuits are operated by gate signals with a timedifferential.

FIG. 6 is a diagram showing the input current waveform when multiplelamps are lighted by switching with the same timing and the same dutycycle.

FIG. 7 is a diagram showing the constitution of the lamp lighting deviceof the second implementation of this invention.

FIG. 8 is a diagram showing the waveforms of parts of the lightingcontrol circuit of the second implementation.

FIG. 9 is a diagram showing an example of the basic structure of an lamplighting device using thyristors.

FIG. 10 is a diagram showing the waveforms of various parts duringcontinuity angle control of the thyristors in FIG. 9.

FIG. 11 is a diagram showing the waveforms of various parts during zerocross control of the thyristors in FIG. 9.

FIG. 12 is a diagram showing the input current, output current andvoltage waveforms during continuity angle control and zero crosscontrol.

FIG. 13 is a diagram showing the waveforms of various parts during useof the alternating current chopper control method.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a diagram showing the constitution of the filament lamplighting device of the first implementation of this invention.

In the drawing, 1 is the lamp lighting device, 20 is an alternatingcurrent power supply, and 2-1 through 2-n are lighting control circuits.The switching elements of lighting control circuits 2-1 through 2-n arecontrolled by gate signals from the controller 3, and light adjustmentof filament lamps 4-1 through 4-n is accomplished by controlling thealternating current inputs fed from the alternating current power supply20.

The controller 3 comprises a gate signal generation circuit 3 a thatsupplies gate signals GATE SIGNAL to the switching elements of thelighting control circuits 2-1 through 2-n, and a CPU 3 b. Based on theoutput of the CPU 3 b, the gate signal generation circuit 3 a generatesthe switching signals shown in FIG. 13(b), and turn ON or OFF theswitching elements of the lighting control circuits 2-1 through 2-n.

The operation of the lamp lighting control circuits shown in FIG. 1 isexplained next.

FIG. 2 is a diagram showing the constitution of an lamp lighting controlcircuit of the implementation shown in FIG. 1; it shows one lamplighting control circuit extracted from those shown in FIG. 1. In thedrawing, 2 is a lighting control circuit, 20 is the alternating currentpower supply, Tr1 through Tr4 are switching elements, D1 through D4 arediodes, Cis a condenser, L is an inductance, and 4 is a filament lamp(hereafter abbreviated as “lamp”).

The switching elements Tr1 through Tr4 are turned ON and OFF with acertain drive frequency, as shown in FIG. 13, by gate signals generatedby the gate signal generation circuit 3 a shown in FIG. 1. Some highfrequency, such as 20 kHz, is chosen for this drive freeqency. If thisfrequency is too low, the capacity of the condenser C on the output sidebecomes too large, and a sound may be produced. If it is too high, onthe other hand, the efficiency of the switching elements deteriorates.It is better to set an appropriate frequency between the two.

The lamp lighting control circuit 2 in FIG. 2 operates as follows.

Commercial alternating current power supply is fed from the alternatingcurrent power supply 20 to the lamp lighting control circuit 2.Sometimes the input current flows in the direction A of FIG. 2, andsometimes in the direction B. In either case, the switching elements arecontrolled as shown in FIG. 3.

(1) When the Input Current Flows in the Direction A

1) The first and third switching elements Tr1, Tr3 are turned ON and theother switching elements Tr2, Tr4 are OFF. The output current flows fromthe first switching element Tr1→inductance L→Lamp 4→fourth diode D4.

2) While the third switching element Tr3 remains ON, the first switchingelement Tr1 is turned OFF and the other switching elements Tr2, Tr4remain OFF. The residual current in the inductance 2 flows from theinductance L→lamp 4→third switching element Tr3→second diode Dischargevessel 2→inductance L.

3) The switching combinations of 1) and 2) above are repeated.

(2) When the Input Current Flows in the Direction B

4) The second and fourth switching elements Tr2, Tr4 are turned ON andthe other switching elements Tr1, Tr3 are OFF. The output current flowsfrom the fourth switching element Tr4→Lamp 4→inductance L→first diodeD1.

5) While the second switching element Tr2 remains ON, the fourthswitching element Tr4 is turned OFF and the other switching elementsTr1, Tr3 remain OFF. The residual current in the inductance L flows fromthe inductance L→second switching element Tr2→third diode Dischargeconcentrator 3→lamp 4→inductance L.

6) The switching combinations of 4) and 5) above are repeated.

By means of the control described above, the waveform of each part ofthe lamp lighting control circuit 2 conforms to that shown in FIG. 13.Now, in this example the lamp lighting control circuit 2 had input froma 50 Hz commercial alternating current power supply, and the switchingfrequency of switching elements Tr1 and Tr4 was 20 kHz.

When the input voltage waveform is the waveform shown in FIG. 13(a), andthe switching duty cycle is about 50%, the switching signal will be asin FIG. 13(b). What is marked (1) in the figure corresponds to thecircuit operation in (1)1) above, and (2) corresponds to the operationin (1)2). Similarly, (4) and (5) correspond to the circuit operations in(2)4) and 5).

By means of the switching described above, the output current waveformof the lamp lighting control circuit 2 is made to conform with that inFIG. 13(c).

That is, during (1) in FIG. 13(b), the current from the commercialalternating current power supply is output as it is, and the lampcurrent value increases gradually. And when the switch is made to (2) ofFIG. 13(b), the output side is cut off from the commercial alternatingcurrent power supply, but because of the residual current in theinductance L, the current flowing to the lamp 4 decreases gradually. Ifthe operation (1) resumes before the residual current has reached zero,the output current increases again. The same is true of (4) and (5).

Now, for the purpose of explanation, the irregularities in FIG. 13(c)have been exaggerated, but in reality, if the switching is done at 20kHz, for example, the irregularities are very small, and the outputwaveform will be sinusoidal even without a filter circuit on the outputside. If the necessity does exist, a clean sine wave as shown in FIG.13(d) can be achieved by flattening irregularities with a condenser C onthe output side.

The ratio of times (1):(2) (or (3):(4)) is called the duty cycle. If theduty cycle were 1, then only circuit operation (1) would transpire, andthe input waveform going to the lamp would be the same as the waveforminput to the lamp lighting device; if the duty cycle were 0, there wouldonly be circuit operation (2), and there would be zero input to thelamp.

Consequently, by varying the switching duty cycle between 0 and 1, it ispossible to obtain an output current with a sinusoidal waveform, withthe peak value varying in the range 0≦(peak output current Ip′)≦(peakinput current Ip). That is, it is possible to supply a continuouslyvariable current to the lamp 4.

On the other hand, because the waveform of the input current to the lamplighting control circuit 2 is repeatedly turned ON/OFF in accordancewith the duty cycle of the switching element, it becomes as in FIG.13(a) (see the shaded parts in the drawing).

As shown in FIG. 13(a), because the switching is at 20 kHz, the inputcurrent to the lamp lighting control circuit 2, has great high-frequencydistortion.

Therefore, the following was done to the switching control of each lamplighting control circuit in this implementation, to reduce thehigh-frequency distortion on the input side.

FIG. 4 is a diagram showing the gate signals of lamp lighting controlcircuits 2-1 through 2-n. The drawing shows the case of n=4.

As shown in the drawing, in this implementation the cycle time T isdivided by the number of lamps, and the switching elements Tr1 throughTr4 of the lamp lighting control circuits 2-1 through 2-n that output totheir lamps are operated in order with that time differential.

Taking as an example the case of lighting four lamps with a switchingfrequency of 20 kHz, there is one lamp lighting control circuit for onelamp, and so there are four lamp lighting control circuits, from 1through 4. In this case, a 20 kHz cycle (cycle length 50 μs) is dividedby 4, and the gate signal time differential is 12.5 μs.

FIG. 5 is a diagram showing the input current waveform when multiplelamp lighting control circuits are operated by gate signals having atime differential like that described above.

In the drawing, when the lamp lighting control circuit 2-1 for lightadjustment of the lamp 4-1 is switched by gate signals, the switchingelements operate with a certain duty cycle, and the input currentwaveform of the lamp lighting control circuit 2-1 is as shown in FIG.5(a).

Then, when the switching element of lamp lighting control circuit 2-2operates 12.5 μs after the operation of lamp lighting control circuit2-1, the input current waveform of the lamp lighting control circuit 2-2is as shown in FIG. 5(b).

Similarly, when the operation moves in order to the lamp lightingcontrol circuit 2-3 and then lighting control circuit 2-4, the inputcurrent waveforms are as in FIG. 5(c) and (d).

Putting together the current waveforms of FIG. 5(a) through (d) producesthe input current waveform for the lamp lighting device as a whole whenlighting multiple lamps. This is the sine wave shown in FIG. 5(e).

For example, if n=4 and the duty cycle is 10%, the input current wouldnot be sinusoidal, but the frequency of the input current would be 80kHz, and the maximum current value would not increase, so it would bepossible to obtain a sine wave using a small filter circuit.

FIG. 6 is the input current waveform in the event that multiple lampsare lighted by switching with the same timing and the same duty cycle.In the drawing, (a), (c), (e) and (g) show the gate signals of the lamplighting control circuits 2-1 through 2-4 for light adjustment of thelamps 4-1 through 4-4, and (b), (d), (f) and (h) show the input currentwaveforms of lamp lighting control circuits 2-1 through 2-4. FIG. 6(i)shows the input current (total) to the lamp lighting control circuits.

In this case, the current values are overlapped as shown in the drawing,and the high-frequency distortion on the power supply side are quitegreat. For that reason it is necessary to have a filter circuit that cancope with large current values and filter. The wave induces 20 kHzhigh-frequency distortion that is a factor that makes the equipmentlarger and increases costs.

FIG. 7 is a diagram showing the constitution of the lamp lighting deviceof the second implementation of this invention.

In FIG. 7, 1 is the lamp lighting device, 10-1 through 10-n are the lamplighting control circuits, 20 is the alternating current power supply,11 is the full-wave rectification circuit, Tr10 is the switchingelement, D10 is a diode, L is an inductance, C is a condenser, 4 is afilament lamp, 3 is a controller, 3 a is a gate signal generationcircuit, and 3 b is a CPU.

The switching element Tr10 in this drawing is turned ON/OFF at a certaindrive frequency by gate signals GATE SIGNAL generated by gate signalgeneration 3 a. As in the first implementation, some high frequency,such as 20 kHz, is chosen for this drive frequency.

In FIG. 7, the lamp lighting control circuits operate as follows.

FIG. 8 is a diagram showing the waveforms of parts of the lightingcontrol circuits 10-1 through 10-n of this implementation. The operationof the lamp lighting control circuits of this implementation will beexplained with reference to this drawing.

Commercial alternating current power supply is fed from the alternatingcurrent power supply 20. The input current is fully rectified by thefull-wave rectification circuit 11, and the fully rectified voltage issupplied to the switching element Tr10 as shown in FIG. 8(a).

1) The switching elements Tr10 is fed an ON signal from the controller3, at which point the output current flows from the full-waverectification circuit 11→switching element Tr10→inductance L→Lamp4→full-wave rectification circuit 11.

2) When first switching element Tr1 is turned OFF, the residual currentin the inductance L flows from the inductance L→lamp 4→diode D10inductance L.

3) The switching combinations of 1) and 2) above are repeated.

By means of the control described above, the waveforms of each part ofthe lamp lighting control circuits 10-1 through 10-n conform to thatshown in FIG. 8. Now, in this example the lamp lighting control circuit2 had input from a 50 Hz commercial alternating current power supply,and the switching frequency of switching elements Tr1 through Tr4 was 20kHz.

When the input voltage waveform is the waveform shown in FIG. 8(a), andthe switching duty cycle is about 50%, the switching signal will be asin FIG. 8(b).

That is, when the switching element Tr10 is turned ON, the current fromthe commercial alternating current power supply is output as it is, andthe lamp current value increases gradually. And when the switchingelement Tr10 is turned off, the output side is cut off from thefull-wave rectification circuit 11, but because of the residual currentin the inductance L, the current flowing to the lamp 4 decreasesgradually. If this Tr10 is turned ON again before the residual currenthas reached zero, the output current increases again.

Now, for the purpose of explanation, the irregularities in FIG. 8(b)have been exaggerated, but in reality, if the switching is done at 20kHz, for example, the irregularities are very small, and the outputwaveform will be sinusoidal even without a filter circuit on the outputside. If the necessity does exist, a clean sine wave as shown in FIG.8(d) can be achieved by flattening irregularities with a condenser C onthe output side.

Consequently, by varying the switching duty cycle of switching elementTr10 between 0 and 1, it is possible to obtain an output current with asinusoidal waveform, with the peak value varying as described above.That is, it is possible to supply a continuously variable current to thelamp 4.

On the other hand, because the waveform of the input current to the lamplighting control circuit 10 is repeatedly turned ON/OFF in accordancewith the duty cycle of the switching element Tr10, it becomes as in FIG.8(c); the input current to the lamp lighting control circuit has awaveform with great high-frequency distortion.

Therefore, in this implementation as in the first implementation, thetiming of the switching control of the lamp lighting control circuitswas staggered to reduce the high-frequency distortion on the input side.

That is, as shown in FIG. 4, the switching frequency is divided by thenumber of lamps, and the switching elements Tr10 of the lamp lightingcontrol circuits 10-1 through 10-n that output to their lamps areoperated in order with that time differential.

Taking as an example the case of lighting four lamps with a switchingfrequency of 20 kHz, there is one lamp lighting control circuit for onelamp, and as described above, a 20 kHz cycle (cycle length 50 μs) isdivided by 4, and the gate signal time differential is 12.5 μs.

If multiple lamp lighting control circuits 10-1 through 10-n areoperated by gate signals having a time differential like that describedabove, then as explained in FIG. 5, when the multiple lamps are lit, theoutput current waveform from the full-wave rectification circuit 11 is afully rectified waveform, and the waveform of the alternating currentinput current of the lamp lighting device as a whole is a sine wave.

In this implementation, as stated above, a fully rectified waveform withvariable peak values can be obtained by switching of a fully rectifiedwaveform by means of the lamp lighting control circuit, and by thatmeans the lamps can be lighted. Therefore, it is possible to achieve thesame effect as in the first implementation, without suddenly impressinga high voltage value on the lamps as in the case of continuity anglecontrol.

Moreover, it is possible to constitute a lamp lighting control circuitwith a single switching element, and thus to simplify the circuitry.

In addition, because the output current drops to a near-zero value atevery half cycle of alternating current input, there is no sustained arclike that in the case of direct current lighting to cause filamentbreakage.

As explained above, the following effects can be achieved through thisinvention.

(1) The output current and output voltage waveforms are sinusoidal andthe height of the peak value can be varied, so that it is possible tovary the output power and control the heat output of multiple filamentlamps. Because the voltage is not suddenly impressed on the lamps, nonoise is produced. There is no rush current flow to the filaments, andso lamp life is prolonged. By varying the duty cycle of the switchingelements it is possible to vary the peak value continuously andinstantly, and so the brightness of the lamps can be varied continuouslyand instantly.

(2) Because the timing of the ON/OFF signals fed to the multiplelighting control circuits is staggered, a filter circuit to eliminatehigh-frequency distortion on the input side is unnecessary or can bemade very small, and it is still possible to make the input currentwaveform sinusoidal. For that reason, it is possible to simplify theconstitution of the equipment, and reduce costs.

Further, due to the lighting control circuit there is no ineffectiveoutput. Therefore, it is possible to obtain a lamp lighting device withhigh efficiency.

FIELD OF INDUSTRIAL USE

The filament lamp lighting device of this invention is used in heattreatment and illumination, and particularly for light irradiation heattreatment equipment for semiconductor wafers.

What is claimed is:
 1. A filament lamp lighting device that has analternating current power supply connected to an input side and lightsmultiple filament lamps by controlling output power from the powersupply, said filament lamp comprising: a lighting control circuit foreach of multiple filament lamps, each lighting control circuit having aswitching element for switching input current that is either sinusoidalcurrent from the power supply or fully rectified input current; and acontroller to control the lighting control circuits, wherein thelighting control circuits contain switching elements that supply inputcurrent to the filament lamps when the respective switching element isin an ON state and residual energy stored in an inductance elementconnected in series to the filament lamp when the switching element isin an OFF state, and continue to supply the filament lamps with outputcurrent by repetition of the ON and OFF states, thus generating nearlythe same output current waveform as the input current waveform, andwherein the controller varies the duty cycle of ON/OFF signals of theswitching elements to vary the peak value of the output current andprovide the lighting control circuits with ON/OFF signals havingstaggered timing.